Solar cell wafer wire bonding method

ABSTRACT

A wire bonding system attaches wires to a solar cell wafer. The wire bonding system includes a feed tube through which a wire is drawn. Rollers contact the wire through openings in the feed tube to facilitate movement of the wire. The wire bonding system includes a soldering heater tip and a wire cutter. The solar cell wafer is placed on a platform, which moves the solar cell wafer. The system has multiple lanes for attaching multiple wires to the solar cell wafer at the same time in parallel operations.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.63/124,970, filed on Dec. 14, 2020, which is incorporated herein byreference in its entirety.

TECHNICAL FIELD

Embodiments of the subject matter described herein relate generally tosolar cell fabrication systems and methods.

BACKGROUND

Solar cells are well known devices for converting light to electricalenergy. A solar cell has a front side that faces the sun during normaloperation to collect solar radiation and a back side opposite the frontside. Solar radiation received by the solar cell creates electricalcharges that may be harnessed to power an external electrical circuit,such as a load.

Solar cells may be fabricated from a silicon wafer. For example, a solarcell wafer may be doped, metallized, cleaved, etc. to yield a pluralityof solar cells. Individual solar cells may be electrically connected andlaminated with other components, such as glass, encapsulant, backsheet,etc., to form a solar module.

Despite their widespread acceptance, solar cells still need to befabricated at low cost and high throughput to be able to commerciallycompete with other sources of energy. Embodiments of the presentinvention pertain to a system and method for attaching wires to solarcells.

BRIEF SUMMARY

In one embodiment, a wire bonding system is configured to attach wiresto a solar cell wafer. The wire bonding system may include a moveableplatform, a heated feed tube, a soldering heater tip, and a wire cutter.The platform supports and moves the solar cell wafer. A wire to beattached to the solar cell wafer comes from a wire source and is drawnthrough the feed tube. Rollers contact the wire through openings in thefeed tube to facilitate at least the initial movement of the wire. Thesoldering heater tip contacts the wire to solder the wire to the solarcell wafer, and the wire cutter cuts the wire to a predetermined length.The system has multiple lanes for attaching multiple wires to the solarcell wafer in parallel operations.

In another embodiment, a method of attaching wires to a solar cell waferincludes soldering a first portion of each of a first plurality of wireson a solar cell wafer. In a first indexing instance, the solar cellwafer is moved to draw the first plurality of wires across the solarcell wafer. After moving the solar cell wafer in the first indexinginstance, a second portion of each of the first plurality of wires issoldered on the solar cell wafer. Each of the first plurality of wiresis then cut. In a second indexing instance, the solar cell wafer ismoved to create a gap between the first plurality of wires and afollowing second plurality of wires on the solar cell wafer. In afollowing soldering step, the first plurality of wires may be solderedon the solar cell wafer along lengths of the first plurality of wires.

These and other features of the present disclosure will be readilyapparent to persons of ordinary skill in the art upon reading theentirety of this disclosure, which includes the accompanying drawingsand claims.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the subject matter may be derived byreferring to the detailed description and claims when considered inconjunction with the following figures, wherein like reference numbersrefer to similar elements throughout the figures. The figures are notdrawn to scale.

FIG. 1 shows a hypercell in accordance with an embodiment of the presentinvention.

FIG. 2 shows an enlarged side cross-sectional view of an interfacebetween overlapping solar cells in accordance with an embodiment of thepresent invention.

FIG. 3 shows an enlarged top portion of a solar cell in accordance withan embodiment of the present invention.

FIG. 4 shows a front view of a hypercell in accordance with anembodiment of the present invention.

FIG. 5 shows a flow diagram of a method of fabricating a hypercell inaccordance with an embodiment of the present invention.

FIG. 6 shows a schematic diagram of a solar cell wafer wire bondingsystem in accordance with an embodiment of the present invention.

FIG. 7 shows a top view of a solar cell wafer wire bonding system inaccordance with an embodiment of the present invention.

FIG. 8 shows an enlarged side view of a wire bonding head assembly and awire feeder of a solar cell wafer wire bonding system in accordance withan embodiment of the present invention.

FIGS. 9-14 illustrate a method of attaching wires to a solar cell waferin accordance with an embodiment of the present invention.

FIG. 15 shows wires that have been attached to a solar cell wafer inaccordance with an embodiment of the present invention.

FIG. 16 shows solar cell wafers with in-line and offset wires inaccordance with embodiments of the present invention.

FIG. 17 shows an enlarged side view of a wire bonding head assembly anda wire feeder of a solar cell wafer wire bonding system in accordancewith an embodiment of the present invention.

FIG. 18 shows a flow diagram of a method of attaching wires to a solarcell wafer in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION

In the present disclosure, numerous specific details are provided, suchas examples of systems, components, and methods, to provide a thoroughunderstanding of embodiments of the invention. Persons of ordinary skillin the art will recognize, however, that the invention can be practicedwithout one or more of the specific details. In other instances,well-known details are not shown or described to avoid obscuring aspectsof the invention.

FIG. 1 shows a hypercell 100 in accordance with an embodiment of thepresent invention. In the example of FIG. 1 , the hypercell 100comprises a plurality of solar cells 120 that are in a shingledarrangement, one overlapping another (see arrow 103) like shingled tileson a roof. The shingled arrangement connects the solar cells 120 inseries to form the hypercell 100. Each solar cell 120 has asemiconductor diode structure and electrical contacts to thesemiconductor diode structure by which electric current generated in thesolar cells 120, when they are illuminated by light, may be provided toan external load.

In one embodiment, each solar cell 120 is a crystalline silicon solarcell having a front side (sun side) with front surface metallizationpatterns and a back side having back surface metallization patterns. Thefront surface and back surface metallization patterns provide electricalcontact to opposite sides of an n-p junction of the solar cell 120. Thefront surface metallization pattern is disposed on a semiconductor layerof n-type conductivity, and the back surface metallization pattern isdisposed on a semiconductor layer of p-type conductivity. As can beappreciated, one or more aspects of the solar cells 120 may be variedwithout detracting from the merits of the present invention. Forexample, the front surface metallization pattern may be disposed on asemiconductor layer of p-type conductivity, and the back surfacemetallization pattern may be disposed on a semiconductor layer of n-typeconductivity.

FIG. 2 shows an enlarged cross-sectional view of an interface (see FIG.1, 103 ) between overlapping solar cells 120 in accordance with anembodiment of the present invention. A solar cell 120 may include asemiconductor substrate 102, a bus bar 110, fingers 106, and wires 108.The semiconductor substrate 102 may comprise a semiconductor layer ofn-type conductivity on the front side and a semiconductor layer ofp-type conductivity on the back side. Free electrons in thesemiconductor layer 102 move from the semiconductor layer 102 throughthe fingers 106, to the wires 108, then to the bus bar 110. From the busbar 110, the electrons may move to an adjacent connected solar cell 120,thus creating current through the hypercell 100.

In one embodiment, the front surface metallization patterns includingthe bus bar 110 and/or fingers 106 are formed from silver paste used forsuch purposes and deposited, for example, by screen printing methods. Ascan be appreciated, the bus bar 110 and/or fingers 106 may also beformed from other suitable materials and deposition methods. In thefigures, only some of the bus bars 110, wires 108, and fingers 106 arelabeled to minimize clutter on the figures.

In the example of FIG. 2 , the back surface metallization pattern of thesolar cell 120 includes a contact pad 116. The contact pad 116 maycomprise the same material and formed the same way as the bus bars 110and/or fingers 106. An electrically conductive adhesive (ECA) 118connects the contact pad 116 of a solar cell 120 to the bus bar 110 ofan adjacent solar cell 120 to create a series electrical connectionbetween the solar cells 120.

FIG. 3 shows an enlarged top portion of a solar cell 120 in accordancewith an embodiment of the present invention. In the example of FIG. 3 ,the fingers 106 are disposed in parallel orientation to the bus bar 110,and the wires 108 are disposed in perpendicular orientation to the busbar 110 and fingers 106. The bus bar 110, wires 108, and fingers 106 areelectrically connected together, which in one embodiment areelectrically connected to a semiconductor layer of n-type conductivity.As can be appreciated, the design of the bus bars 110, fingers 106, andwires 108 may be varied to suit different hypercell designs.

FIG. 4 shows a front view of the hypercell 100 in accordance with anembodiment of the present invention. In the example of FIG. 4 , thehypercell 100 is depicted as having three shingled solar cells 120 forillustration purposes only. As can be appreciated, the number of solarcells in a hypercell depends on the particulars of the hypercell. Asillustrated in FIG. 4 , each solar cell 120 has a plurality of wires108, with each wire 108 having ends that terminate on the solar cell120. The bus bars 110 and fingers 106 may be formed by printing or otherdeposition methods. In contrast, the wires 108 are individually pulledfrom a wire source, placed (as opposed to deposited) on the front sidesof the solar cells 120, and then soldered to the fingers 106 and busbars 110. Accordingly, attaching wires 108 to solar cells 120 can be acostly and time consuming operation.

FIG. 5 shows a flow diagram of a method 251 of fabricating a hypercell100 in accordance with an embodiment of the present invention. In theexample of FIG. 5 , a solar cell wafer is received in a solar cell waferwire bonding system (step 252). In one embodiment, the solar cell wafer,as received in the wire bonding system, already has bus bars, fingers,and a semiconductor diode structure. The wire bonding system attacheswires to the solar cell wafer (step 253) before the solar cell wafer iscleaved into individual strips of solar cells. The solar cell wafer isthereafter removed from the wire bonding system. In a laser system orother tool, scribe lines are formed on the solar cell wafer (step 254).The scribing step may be performed by scanning a laser beam on the solarcell wafer to form scribe lines thereon. The scribe lines facilitatecleaving of the solar cell wafer in a subsequent step to form individualstrips of solar cells. ECA's are thereafter printed on contact pads ofthe solar cell wafer (step 255). The solar cell wafer is then cleavedalong the scribe lines to yield strips of solar cells (step 256), whichare then shingled into a hypercell (step 257). The shingled solar cellsmay be cured thereafter.

FIG. 6 shows a schematic diagram of a solar cell wafer wire bondingsystem 200 in accordance with an embodiment of the present invention.FIG. 6 shows a top view, a side view, and a front view of the wirebonding system 200. The wire bonding system 200 is configured to attacha plurality of wires 108 (e.g., see FIG. 3 ) on a solar cell wafer 250.The wires 108 are attached to the solar cell wafer 250 before the solarcell wafer 250 is cleaved into individual strips of solar cells 120.

The wire bonding system 200 includes a platform 210, which rides on anX-axis (front and back) translation stage 211 and a Y-axis (left andright) translation stage 212. Motors and guides of the translationstages are not shown for clarity of illustration. The solar cell wafer250 is placed on the platform 210. Actuating the translation stages 211and 212 moves the platform 210, and thus the solar cell wafer 250, alongan X-Y plane that is parallel to the ground. This allows attachment ofthe wires 108 in-line or offset.

The wire bonding system 200 includes a wire feeder 240 that isconfigured to receive a plurality of wires 108 that are to be attachedto the solar cell wafer 250. A wire bonding head assembly 230 canaccommodate a plurality of lanes, with each lane being configured toplace, solder, and cut a single wire 108 on the solar cell wafer 250.

The head assembly 230 and feeder 240 are mounted on a block 220, whichis actuated by a pillar 221. Each end of the block 220 is coupled to apillar 221, but only one pillar 221 is shown for clarity ofillustration. The pillar 221 is configured to move the block 220 (andthus the head assembly 230 and feeder 240) along the Z-axis (up anddown) and to rotate the block 220 (see theta) to change the angle of thehead assembly 230 and feeder 240 relative to the plane of the solar cellwafer 250. The pillar 221 may comprise translational and rotationalmotors and corresponding guides (not shown).

FIG. 7 shows a top view of the wire bonding system 200 in accordancewith an embodiment of the present invention. The wire bonding system 200includes a computer 270 that executes a control program 271 forcontrolling the operation of the wire bonding system 200. The computer270 may include interface ports for communicating with motorcontrollers, transducers, sensors, and other control components of thewire bonding system 200. The computer 270 and the control components ofthe wire bonding system 200 may be implemented using suitable componentsthat are commonly employed in the field of industrial control andautomation.

As illustrated in FIG. 7 , the wire bonding system 200 has a pluralityof lanes for attaching a plurality of wires 108 on the solar cell wafer250, which is supported by the platform 210. A wire source provides aplurality of wires 108, which are inserted in corresponding feed tubes(see FIG. 8, 304 ) of the wire feeder 240 (see arrow 261). In oneembodiment, the wire source provides copper wires 108 that are coatedwith tin and lead. The wires 108 may be pulled through a clean fluxsolution (not shown) before being soldered to the solar cell wafer 250in the wire bonding system 200.

On each lane of the wire bonding system 200, a wire 108 is moved throughthe wire feeder 240 in the X-axis direction (see arrow 262), soldered bya corresponding heater tip 231 (see also FIG. 8, 231 ), and cut by acorresponding cutter 232 (see also FIG. 8, 232 ). In the example of FIG.7 , the cutter 232 is adjacent to the heater tip 231. The plurality oflanes allows a plurality of wires 108 to be attached to the solar cellwafer 250 at the same time in parallel operations, thereby increasingthroughput. The wire bonding system 200 may be scaled to accommodatehypercell designs with fewer or more wires 108 and/or different solarcell wafer dimensions.

FIG. 8 shows an enlarged side view of a wire bonding head assembly 230and a wire feeder 240 of the wire bonding system 200 in accordance withan embodiment of the present invention. FIG. 8 shows a single lane forattaching a wire 108 to the solar cell wafer 250. As previously noted,the wire bonding system 200 has multiple lanes for attaching multiplewires 108 at the same time in parallel operations.

In the example of FIG. 8 , the wire feeder 240 comprises a feed tube 304and a plurality of motorized rollers 303. In one embodiment, the feedtube 304 is heated and can accommodate a wire 108 that has a diameterranging from 100 μm to 600 μm. The feed tube 304 may have an entrydiameter that is larger than the diameter of the wire 108 to facilitatewire insertion, and an exit diameter that is slightly larger (e.g.,about 5% larger) than the diameter of the wire 108. The feed tube 304 isat an angle relative to the solar cell wafer 250. The wire 108 comesfrom the wire source, enters the feed tube 304 on one end, and exits thefeed tube 304 on an opposite end in the vicinity of the head assembly230. The feed tube 304 has openings through which the rollers 303contact the wire 108 in the feed tube 304. In the example of FIG. 8 , apair of opposing rollers 303 contact the wire 108 to facilitate movementof the wire 108 in the feed tube 304. The rollers 303 may be coupled tomotors (not shown) with a brake system. The motors can be controlled todrive the rollers 303 to push or pull the wires 108 through the feedtube 304. Two pairs of opposing rollers 303 are shown for illustrationpurposes.

In the example of FIG. 8 , an exit end of the feed tube 304 is below thehead assembly 230 in the vicinity of an attachment point (see 305) wherethe wire 108 is soldered to the solar cell wafer 250. In one embodiment,the attachment point may be on a bus bar or a soldering pad. The headassembly 230 includes a soldering heater tip 231 and a cutter 232. Atthe attachment point, the heater tip 231 is heated (e.g., by pulseheating) to solder the wire 108 to the attachment point on the solarcell wafer 250. The soldering performed using the heater tip 231 may bean initial soldering step (also referred to as “first stage soldering”)to align and tack the wire 108 on the solar cell wafer 250. The cutter232 is configured to cut the wire 108 after soldering. The platform 210(see FIG. 6 ) that supports the solar cell wafer 250 is moved forward(see arrow 311) to move the solar cell wafer 250 relative to the headassembly 230 and wire feeder 240 as needed.

A final soldering step (also referred to as “second stage soldering”)may follow the initial soldering step. The final soldering step maysolder the wire 108 to the solar cell wafer 250 along a length of thewire 108 that has not been soldered to the solar cell wafer 250 duringthe initial soldering step. The final soldering step may be performed,for example, by infrared soldering after the head assembly 230. Thefinal soldering step may be performed in a heated chamber, such as anoven, for example. The final soldering step may also be performed in adedicated soldering station that is integrated with or separate from thewire bonding system 200. The final soldering step may involve placingthe solar cell wafer 250 on a heated platform, with the wires 108 facingaway from the platform, and then pressing the wires 108 (e.g., using arounded tip or metal roller) toward the platform. The solar cell wafer250 may also be placed with the wires 108 facing a heated chuck, andthen pressing down on the solar cell wafer 250 to make the wires 108contact the chuck.

FIGS. 9-14 illustrate a method of attaching wires to a solar cell waferin accordance with an embodiment of the present invention. The method isexplained using components of the wire bonding system 200 forillustration purposes. As can be appreciated, the method may also beperformed using other components without detracting from the merits ofthe present invention.

In the example of FIGS. 9-14 , the steps of the method are performedsequentially. In a first step illustrated by FIG. 9 , a wire 108 is fedthrough the feed tube 304 (see arrow 312). The rollers 303 facilitate atleast the initial movement of the wire 108 in the feed tube 304. A firstend of the wire 108 exits the feed tube 304 in the vicinity of the headassembly 230.

In a second step illustrated by FIG. 10 , the heater tip 231 is loweredto contact and solder (e.g., by pulse heating) the first end of the wire108 to a first attachment point on the solar cell wafer 250. The heatertip 231 is thereafter raised back to its neutral position.

In a third step illustrated by FIG. 11 , the wire 108 is moved throughthe feed tube 304 (see arrow 313) and the solar cell wafer 250 isindexed to move forward a predetermined distance (see arrow 314),thereby drawing a predetermined length of the wire 108 over the solarcell wafer 250. For example, the solar cell wafer 250 may be indexed tomove a distance of 30 mm to 70 mm for six to two cuts on the solar cellwafer 250, with a cut providing a continuous wire 108. The total lengthof a wire 108 depends on the design of the hypercell. In the third step,the wire 108 is drawn primarily due to the movement of the solar cellwafer 250. As noted, the solar cell wafer 250 is supported on theplatform 210, which is moved to move the solar cell wafer 250.

In a fourth step illustrated by FIG. 12 , the heater tip is lowered tocontact and solder the wire 108 to a second attachment point on thesolar cell wafer 250. The heater tip 231 is thereafter raised back toits neutral position. In this example, the wire 108 is tack soldered totwo attachment points, which are on opposing ends of a wire 108. As canbe appreciated, the wire 108 may also be tack soldered to additionalattachment points on the solar cell wafer, for example to a thirdattachment point between the first and second attachment points.

In a fifth step illustrated by FIG. 13 , the cutter 232 is lowered tocut the wire 108, thereby forming a second end of the wire 108 at thesecond attachment point. The cutter 232 is thereafter raised back to itsneutral position. At this time, the wire 108 has a predetermined totallength with first and second ends that are soldered to the solar cellwafer 250.

In a sixth step illustrated by FIG. 14 , the solar cell wafer 250 isindexed to move forward a predetermined distance (see arrow 315),thereby creating a gap of predetermined gap length between the wire 108and the next following wire 108. The number of gaps and the length ofthe gap depend on the design of the hypercell. For example, the wirebonding system 200 may create two gaps. A gap within a solar cell wafermay have a gap length of 0.5 mm to 3 mm, and a gap between solar cellwafers may have a gap length of 2 mm to 6 mm.

From the sixth step, the method proceeds back to the first step (seeFIG. 9 ) to attach the next following wire 108 onto the solar cell wafer250. As can be appreciated, the method is able to attach the wires 108continuously and without wasting wire materials, thus minimizingmaterial cost and attachment time.

FIG. 15 shows wires 108 that have been attached to a solar cell wafer250 in accordance with an embodiment of the present invention. Only twowires 108 are shown for clarity of illustration. In the example of FIG.15 , the wires 108 are perpendicular to the fingers 106. The wires 108are soldered to attachment points 320 during initial soldering steps asillustrated in FIGS. 10 and 12 . An attachment point 320 may be a busbar or a soldering pad, for example. In the example of FIG. 15 , thewire 108 is also soldered to an attachment point 320 in the middleportion of the wire 108. During a final soldering step, the lengths L1and L2 of the wire 108 are soldered to the solar cell wafer 250. A gapG1 is created between the wire 108 and a following wire 108 when thesolar cell wafer 250 is moved to pull the wire 108 after cutting asillustrated in FIG. 14 .

The wires 108 may be attached along straight or offset lanes. FIG. 16shows a solar cell wafer 250-1 where the wires 108 are attached alongstraight lanes. In the solar cell wafer 250-1, a wire 108 is in-linewith the next following wire 108. FIG. 16 also shows a solar cell wafer250-2 where the wires 108 are attached along offset lanes. In the solarcell wafer 250-2, a wire 108 and a next following wire 108 are offset.The wires 108 may be attached at offset lanes by moving the solar cellwafer 250 or the head assembly 230 and wire feeder 240 along the Y-axisas needed.

The wire bonding system 200 may be adapted to meet the needs ofdifferent hypercell designs. For example, the wire bonding system 200may be adapted to accommodate different wire gauges. FIG. 17 shows anenlarged side view of a wire feeder 240-1 of the wire bonding system 200in accordance with an embodiment of the present invention. The wirefeeder 240-1 is an embodiment of the wire feeder 240 (see FIG. 8 ) thatcan accommodate thinner wires 108, e.g., 100 μm to 400 μm diameter.

In the example of FIG. 17 , the feed tube 407 is a capillary tube thataccepts a thin wire 108. As in the previously described feed tube 304,the feed tube 407 has openings through which motorized rollers 405 and406 contact the wire 108 in the feed tube 407. In the example of FIG. 17, the rollers 405 are rubber rollers whereas the rollers 406 are groovedrollers. A pair of opposing roller 405 and roller 406 facilitatemovement of the wire 108 through the feed tube 407. As shown in azoom-in view 409 of FIG. 17 , a roller 406 may have a V-shaped groove.The wire 108 goes through a space (see 408) between the roller 405 andthe V-shaped groove of the roller 406, keeping the thin wire 108 inproper alignment.

FIG. 18 shows a flow diagram of a method 500 of attaching wires to asolar cell wafer in accordance with an embodiment of the presentinvention. The method 500 may be performed using previously-describedcomponents. As can be appreciated, other components may also be employedwithout detracting from the merits of the present invention.

In the method 500, a wire is fed through a feed tube of a solar cellwafer wire bonding system (step 501). At an exit end of the feed tube, afirst portion of the wire is soldered to a first attachment point on asolar cell wafer (step 502). The solar cell wafer is thereafter movedforward, thereby drawing the wire through the feed tube and across thewafer (step 503). A second portion of the wire, at the exit of the feedtube, is soldered to a second attachment point on the wafer (step 504).Generally, the wire may be soldered to a plurality of attachment pointson the wafer, such as on two, three, etc. attachment points. The wire isthereafter cut to form a continuous length of the wire on the solar cellwafer (step 505). The solar cell wafer is then moved forward to create agap between the wire and a next following wire to be attached to thesolar cell wafer (step 506). The rest of the wire, such as portions ofthe wire that have not been soldered to attachment points, is thensoldered to the solar cell wafer (step 507).

A solar cell wafer wire bonding system and a method of attaching wiresto a solar cell wafer have been disclosed. While specific embodiments ofthe present invention have been provided, it is to be understood thatthese embodiments are for illustration purposes and not limiting. Manyadditional embodiments will be apparent to persons of ordinary skill inthe art reading this disclosure.

What is claimed is:
 1. A method of attaching wires to a solar cellwafer, the method comprising: soldering a first portion of each of afirst plurality of wires on a solar cell wafer; in a first instance,moving the solar cell wafer to draw the first plurality of wires acrossthe solar cell wafer; after moving the solar cell wafer in the firstinstance, soldering a second portion of each of the first plurality ofwires on the solar cell wafer; cutting each of the first plurality ofwires; and in a second instance, moving the solar cell wafer to create agap between the first plurality of wires and a second plurality of wireson the solar cell wafer.
 2. The method of claim 1, further comprising:soldering the first plurality of wires on the solar cell wafer along alength of each of the first plurality wires.
 3. The method of claim 1,wherein the first portion of each of the first plurality of wires issoldered on a corresponding attachment point on the solar cell wafer. 4.The method of claim 3, wherein the attachment point is a bus bar.
 5. Themethod of claim 3, wherein the attachment point is a soldering pad. 6.The method of claim 1, wherein soldering the first portion of each ofthe first plurality of wires on the solar cell comprises: drawing eachof the first plurality of wires through a corresponding feed tube of aplurality of feed tubes; and soldering the first portion of each of thefirst plurality of wires at an exit end of the corresponding feed tubeof the plurality of feed tubes.
 7. The method of claim 6, whereincutting each of the first plurality of wires comprises: cutting each ofthe first plurality of wires at the exit end of the corresponding feedtube of the plurality of feed tubes.